1. Field of the Invention
The present invention relates to a data generation apparatus, an inkjet recording apparatus configured to perform recording by discharging pigment ink, and a data generation method.
2. Description of the Related Art
To meet growing demands for high resistance to light and water of recorded images, efforts are being directed toward development of an inkjet recording apparatus which uses ink containing pigments as a color material. Generally, a recording medium, such as glossy paper, has tiny pores formed on its surface to improve both absorption of an ink solvent and fixation of the color material. When dye ink is used, since the dye as a color material is absorbed through the pores simultaneously with absorption of water content, the dye penetrates into the inside of the recording medium.
On the other hand, when pigment ink is used, the pigment as a color material does not readily penetrate into the inside of the recording medium. This is because the pigment is hard to dissolve in water and is dispersed as fine particles in water, and those particles are larger than the pores of the surface of the recording medium. Therefore, when pigment ink is used, pigment molecules are deposited on the surface of the recording medium and fixed. Therefore, the smoothness of the surface of the recording medium is reduced, thus decreasing the glossiness of the printed image. The larger the amount of ink becomes, the thicker the ink dots are deposited, reducing the surface smoothness of a recording medium, so that the gloss tends to be reduced. The reduction in the gloss gives rise to relative gloss differences over the whole recorded image, and the irregularity of the gloss is noticeable.
As a solution to the issue of the uneven gloss of pigment ink, Japanese Patent Application Laid-Open No. 2008-162095 discusses a method for obtaining an even gloss on recorded images by using mask patterns of different degrees of dispersion according to gloss characteristics inherent to respective types of ink and also to their contour differences at the time of fixation.
The inventors of the present invention have found that the gloss irregularity is caused not only by a decrease in the glossiness due to deposition of the pigment on the surface of the recording medium. The finding is as follows.
In the areas of a recorded image, where a small number of ink dots are applied, most of the ink dots are not overlaid one on top of each other, but the ink dots are present independently of each other. At this point in time, the pigment is deposited on the surface, but a dispersing resin used to disperse the pigment in the ink mostly penetrates into the inside of the recording medium. Similarly, high-molecular compounds added for other purposes penetrate. Consequently, the pigment is often exposed at a colored layer as the outermost layer.
On the other hand, in the areas of a recorded image, where a large number of ink dots are applied, as described above, the pigment is deposited on the surface of the recording medium with undulations. At this time, owing to the filler-effects of the pigment-colored layer as the base coat, a dispersing resin and high-molecular compounds included in the ink hardly penetrate either into the pigment colored layer or the recording medium, and are fixed as they are deposited on the surface. Therefore, the outermost layer of the colored layer contains relatively high contents of the dispersing resin and the high-molecular compounds.
Dominant factors of the glossiness of recorded images are surface smoothness and surface reflectance. Generally, pigments have a reflectance higher than that of resins and high-molecular compounds. Therefore, in the areas where a small number of ink dots are applied, the gloss is high because the pigment is deposited in large amounts on the outermost layer. On the other hand, in the areas where a large number of ink dots are applied, since a resin and high-molecular compounds remain on the outermost layer, the undulations on the surface contribute to a reduction of surface smoothness, and the gloss is reduced.
As described above, in a recorded image printed with pigment ink, in the areas where a large number of ink dots are applied, the gloss is low, and in the areas where a small number of ink dots are applied, the gloss is high. Therefore, the uneven gloss of a recorded image is noticeable as the irregularity of the gloss.